Visual assessment of the concrete vaults which surround underground waste storage tanks

摘要

Radioactive waste produced at the Savannah River Site (SRS) is stored in underground tanks. There are four different waste tank designs. For each waste tank design the outermost containment shield between the waste and the soil is a concrete vault surrounding the carbon steel liner(s). Should the primary and/or secondary liner be breached, the concrete vault would slow transport of the waste so that contamination of the soil is minimized. The type 3 waste tanks have a stated design life of 40--60 years. With the uncertainty of the schedule for transfer of the waste to the Defense Waste Processing Facility, it is conceivable that the tanks will be required to function past their design life. The Department of Energy formed a Waste Tank Structural Integrity Panel to investigate the potential for aging and degradation of underground radioactive waste storage tanks employed in the weapons complex. The panel is focusing on how each site in the complex: (1) inspects the waste tanks for degradation, (2) understands the potential degradation mechanisms which may occur at their sites, and (3) mitigates the known potential degradation mechanisms. In addition to the carbon steel liners, the degradation of the concrete vault has also been addressed by the panel. High Level Waste Engineering (HLWE) at SRS has formed a task team to identify key issues that determine and/or effect the condition of the concrete. In June 1993, slides were reviewed which showed the inside of the concrete vault in Type 1, 2, and 4 tanks. The authors subsequently visited the tank farm and assessed the visible portions of the outer concrete vault. Later a team of engineers knowledgeable in concrete degradation performed a walk-down. Photographs showing the concrete condition were taken at this time. This report summarizes the findings of these walk-downs and reinforces previous recommendations.